1. Field of the Invention
The present invention relates to a lamp assembly, and more particularly, to an improved incandescent lamp assembly with a screw-in base that is durable, resistant to shocks and vibrations, heat resistant, and long lasting. The lamp assembly also ensures convenience and ease of manufacture and assembly.
2. Description of the Prior Art
Although not necessarily limited thereto, the invention has particular application to and will be described with reference to an incandescent lamp for general use.
In conventional incandescent lamp assemblies it is common practice to provide a threaded screw-in base to be connected with an outer bulbous envelope.
The bulbous envelope is usually shaped into a generally elliptical or round globe having a cylindrically extending neck. To the neck of the envelope is fused and combined with a glass stem mount having a pair of lead-in wires between which a tungsten filament is bridged. A conventional screw-in base is secured around a mold portion by means of a cement by which it is connected to the neck of the envelope. The primary components of the conventional cement are: marble flour (approximately 80% of the total weight), phenol resin, pine resin, silicon resin, shellac, and hardener.
Although the bond between the two components is designed to hold for the lifetime of the lamp, it is subject to breakdown because the cement is often vulnerable to heat generated at the filament and to humidity from the ambient air. With the lapse of hundreds of hours of operation the cement will absorb humidity from the ambient air and deteriorate and tend to give way.
Also, since incandescent lamps are occasionally mounted and dismounted by the users, shearing forces recurringly develop between the neck of the envelope and the inner surface of the metal screw-in base, causing cracks within the cement, which results in a loose bond, or worse, separation.
A loosely fit base poses a serious hazard to the lamp users, particularly when the lamp is in use with the screw-in base above the envelope; the fragile glass envelope may then fall upon the users.
Japanese Utility Model Publication No. 43-8930 (Shimazu) discloses an assembly of an incandescent lamp in which the neck is provided with four circumferentially and substantially equally spaced-apart outwardly protruded ridges, each further having a projection at its extreme. In the same vein, the screw-in base is provided with a housing cap which has adjacent its flared rim four circumferentially and substantially equally spaced-apart outwardly protruded ridges.
The protruded ridges extend longitudinally, each also having a further external projection at the lower end. The ridges and the projections are formed to fit those of the envelope neck. Thus when they are assembled the lamp assembly is most likely resistant to longitudinal and revolving forces.
On the other hand, however, it has been found that in large scale production of lamps of such type it is extremely time and labor-consuming to adjust the positions of the ridges for proper alignment, so that there has resulted a severe reduction of productivity.
Also in the prior art, one of the lead-in wires was welded to the screwshell for firm electrical contact. But welding required substantial time and labor.
The Japanese Utility Model Publication No. 52-22955 shows a small lamp assembly which is generally used as a light source used outdoors during road repairs and maintenance. The lamp is entirely housed in a resin shock-absorbing covering. Such a lamp assembly eliminated the need for welding the lead-in wire by providing a small allowance between the outer diameter of the neck of the covering and the inner diameter of the screwshell, with the neck being tapered or stepped to permit the screw-in base to be inserted upwards. The dimension of the margin between the neck and the screw-in base is such that the two components apply appropriate pressure to keep the lead-in wire interposed therebetween.
Nevertheless, upon application of external force on the covering or on the screw-in base, the connection may slip and fail. Also, since the covering is made of resin it is vulnerable to heat and hence the technology is suited only to lamps with low light output, which produce less heat.